PHYSICAL PROPERTIES OF NUCLEIC ACIDS 453 



NHo O 



CH CH 



I I 



CH2OH CH2OH 



XI XII 



Ce — N, is short (1.31 A.), suggesting that it participates in the resonance 

 of the pyrimidine ring. Four of the atoms of the D-ribose ring lie nearly in 

 one plane, viz., Ci , Oi , C2 , and C4 , but the fifth atom of the ring, C3 , is out 

 of the plane l)y nearly 0.5 A. The central bond, N3 — Ci , joining the pyrimi- 

 dine ring to the sugar radical has a length of 1.47 A. and is clearly a single 

 bond. This bond lies in the plane of the pyrimidine ring and forms angles 

 of 109° and 115° with the adjacent ring bonds in D-ribose. Contrary to the 

 previous assumption that the two rings were parallel [see Astbury"], it is 

 evident that they are approximately perpendicular. The bearing of this 



" W. T. Astbury, Symposia Soc. Exptl. Biol. 1, 66 (1947). 



